Method of making assemblies of stainless steel tubing

ABSTRACT

A method of making assemblies of stainless steel tubing or piping and conventional plumbing fittings which comprises coating stainless steel tubing, at least at the ends thereof, with copper, tin or alloys thereof and joining a fitting coated portion by soldering.

United States Patent Ziemianski [451 June 27, 1972 [72] Inventor: John P. Ziemianski, Avonmore, Pa.

[73] Assignee: Allegheny Ludlum Steel Corporation, Pittsburgh, Pa.

[22] Filed: Feb. 26, 1969 [21] Appl.No.: 802,671

[52] US. Cl.... ..29/492, 29/504, 29/196.3 [51] Int. Cl ..B23k 31/02 [58] Field of Search ..29/196.3, 492, 502, 504, 196.4; ll7/50,5l, 114,131

[56] References Cited UNITED STATES PATENTS 2,224,145 12/1940 Dugan et a1 ..29/502 X 2,346,413 4/ 1944 Broecker 29/502 X 2,466,890 4/1949 Gilbertson ..117/50 2,632,943 3/1953 Collins 29/502 X 2,727,834 12/1955 Cape et al.... ..ll7/l31 2,937,438 5/1960 Lemon ..29/502 X 2,940,867 6/ 1 960 Streicher ..1 17/50 X 3,032,870 5/1962 Rohberg et al.... ..29/502 X 3,105,293 10/1963 Skinner et al ..29/492 X 3,286,341 12/1966 Miller ..29/502 X 1,840,724 1/1932 Koehring ..29/492 X OTHER PUBLICATIONS Soldering Manual, American Welding Society publication, copyright 1959, p. 103 Metals Handbook, Vol. 2, 8th Edition, Taylor Lyman Editor, pp. 475, 503, 599- 606 Primary Examiner-John F. Campbell Assistant Examiner-Ronald J. Shore Attorney-Richard S. Speer and Vincent G. Gioia [57] ABSTRACT A method of making assemblies of stainless steel tubing or piping and conventional plumbing fittings which comprises coating stainless steel tubing, at least at the ends thereof, with copper, tin or alloys thereof and joining a fitting coated portion by soldering,

2 Claims, No Drawings METHOD OF MAKING ASSEMBLIES F STAINLESS STEEL TUBING This invention relates to stainless steel tubing for plumbing applications. More particularly, the invention relates to a method of un'lizing stainless steel tubing with conventional copper and copper alloy plumbing fittings.

Stainless steel equipment as fabricated from sheet, strip and tubing has been in use for over thirty years in the chemical engineering, food and dairy industries. These handle a wide variety of liquids, many of which are highly corrosive or, as in the case of milk, require the highest possible standards of hygrene.

For sometime it has been proposed to use stainless steel tubing or piping (as used herein these terms are synonymous) in the plumbing industry as a replacement for the more expensive copper and copper alloy tubing. Initial efforts to use stainless steel in these applications were thwarted by the cost of the tubing, high cost of auxiliary hardware, i.e., fittings, and relative difiiculty in soldering stainless steel tubing. Recent advances in steel making have enabled stainless steel tubing to be produced which may compete in the plumbing industry, however, the problem still remained of joining the stainless steel tubing to fittings of copper and copper alloy. For this purpose it has been suggested to use fluxes for soldering the copper fitting and the stainless steel tubing, however, such fluxes are frequently corrosive and do not hold up well in the environments to which the assemblies are exposed.

An additional problem in the use of stainless steel tubing for plumbing applications is the necessity of educating the plumbers and installers of the stainless steel tubing to the techniques of soldering stainless steel. The acceptance of stainless steel tubing is materially reduced where special practices and techniques must be employed. For the above and other reasons the acceptability of stainless steel tubing in plumbing applications has been materially limited. Recent technological advances now make possible the use of stainless for domestic water service at a cost competitive with current plumbing materials, i.e., light well as-welded tubing.

The present invention provides a method of assembling stainless steel tubing and conventional fittings, e.g., copper or copper alloy fittings, which avoids the problems associated with the previous eflorts to use stainless steel tubing. By practicing the invention, normal soldering techniques with copper tubing presently employed by plumbers may be used to join stainless steel tubing to copper and copper alloy fittings. in accordance with the invention stainless steel tubing is coated with copper, tin, or alloys thereof such as brass or terne, at least at the ends thereof, and fittings of copper or copper alloy are soldered to the stainless steel tubing at the coated portions.

In practicing the invention a variety of stainless steels may be employed and for many applications Type 304 stainless steel is satisfactory. However, in some cases, as for example for use with water containing considerable chlorine, some stress corrosion problem may result. The environmental conditions of both hot and cold water with chlorine contents as high as 100 ppm require a relatively high chromium ferritic grade of stainless steel. Conventional austenitic grades cannot be used because the combination of relatively high temperatures (exceeding 140 F) and the presence of chlorine, under line pressure, can conceivably result in stress corrosion failures. Unfortunately, standard ferritic grades are incapable of being welded due to attendant grain coarsening, embrittlement and drastically decreased corrosion resistance, particularly at the fusion zone. Titanium additions to base ferritic materials circumvent these problems, and the following steel is strongly preferred for use in accordance with the invention.

10 times Carbon/up to 1.3% up to 0.2%

Titanium Aluminum The high cost of stainless steel fittings can be circumvented by utilizing low cost copper base fittings with no fear of galvanic corrosion. The problem of corrosive fluxes solderability would still exist and would be necessary unless the stainless steel tubing is assembled in accordance with the invention. Stainless steel does not acquire its corrosion resistance inherently but is due to a passive transparent oxide film. Efi'ective soldering requires the employment of aggressive, corrosive fluxes (zinc chloride bearing) to remove (activate) the passive oxide film. This practice is necessary to insure metallurgical alloying and bonding so as to permit flow necessary for high strength integral joints. However, this operation must be followed by immediate thorough rinsing and/or neutralizing to remove any flux residue which can conceivably lead to premature pitting and failure. Such rinsing and washing is, of course, somewhat impractical in plumbing applications.

The present invention avoids the need for aggressive, i.e., corrosive fluxes necessary to solder stainless steel by plating and/or coating the stainless steel tubing with a metal and/or alloy system which is inherently solderable, i.e., does not require aggressive type fluxes, namely copper and tin and alloys thereof such as teme or brass. In order to avoid plumber/installer re-education and thereby reduce the acceptability of stainless due to new techniques for soldering, the utilization of a copper coated product in conjunction with conventional copper/brass fittings is appropriate. By practicing the invention, normal soldering techniques currently employed with copper tubing can be used when utilizing this product. Standard plumbers tools, including cut-ofl, solders and fluxes need not be altered to any degree.

The coating, e. g., copper or copper alloy may be applied to the stainless steel in any suitable manner, however, it is presently preferred to copper plate the stainless steel tubing. The plating may be performed relatively easily and provides a coating on the stainless steel tubing which enables the tubing to be satisfactorily soldered to copper and copper alloy fittings. The copper and copper alloy fittings may be any of the type conventionally used in plumbing applications and it is not necessary to employ special fluxes for soldering.

The following is a schedule of tube sizes which compares typical copper tubing and plated stainless.

STANDARD WEIGHT STEEL PIPE As mentioned above, in making assemblies of stainless steel tubing to which has been plated copper or copper alloy, e.g., brass, the tubing may be used with regular cast or wrought copper fittings in such a manner as to enable a plumber to sweat a joint by substantially the same practice as that heretofore used in sweating copper tubing to copper fittings. Moreover a standard plumber's cutofi tool may be used which in effect peens the copper over the edge of stainless steel tubing so as to provide a continuous surface layer of copper. A copper coating of 0.0001 to 0.0003 inch in thickness applied to the stainless steel tubing has proven satisfactory.

In addition to the foregoing it is apparent that advantages of the invention include lower material cost, equivalent installation cost when compared to copper and lower installation cost in comparison to threaded joint systems. Stainless steel tubing also affords inherently higher corrosion resistance, particularly in CO containing potable waters, absence of tuberculation and minimal scale buildup due to deposition of various minerals.

I claim:

1, A method of making an assembly suitable for plumbing applications which comprises electroplating a tube of stainless steel, at least at the end thereof, with a metal selected from the group consisting of copper and alloys thereof, and joining a copper or copper alloy fitting to the stainless steel tube at the coated portion thereof by soldering said fitting to said tube using soldering techniques normally employed for joining two copper members to one another, wherein said stainless steel tube consists essentially of up to 0.07 percent carbon, 0.2 to 0.5 percent manganese, 0.2 to 0.5 percent silicon, l7.5 to 19.0 percent chromium, up to 0.5 percent nickel, 10 times carbon up to 1.3 percent titanium, up to 0.2 percent aluminum, balance iron.

2. A method according to claim 1 wherein said coating metal is copper and is applied to said stainless steel tube by electroplating said stainless tube to a thickness of 0.0001 to 0.0003 inches of electrodeposited copper.

Dedication 3,672,036.J07m P. Zz'emz'anslcz', Avonmore, Pa. METHOD OF MAKING AS- SEMBLIES OF STAINLESS STEEL TUBING. Patent dated June 27 197 2. Dedication filed Oct. 24, 1973, by the assignee Allegheny LudZum lnclustfies, Inc.

Hereby dedicates t0 the Public the entire term of said patent.

[Oyfioz'al Gazette Febmav'y 5, 1974] 

2. A method according to claim 1 wherein said coating metal is copper and is applied to said stainless steel tube by electroplating said stainless tube to a thickness of 0.0001 to 0.0003 inches of electrodeposited copper. 